Bi-metal actuated bi-metal shunt



June 20, 1961 J. H. LEONARD 2,989,605

BI-METAL ACTUATED BI-METAL sHUNT Filed June 5, 1958 2 Sheets-Sheet 1June 20, 1961 J, H, LEONARD 2,989,605

BJI-METAL ACTUATED BI-METAL SHUNT Filed June 5, 1958 2 Sheets-Sheet 2United States Patent O 2,989,605 BI-METAL ACTUATED BI-METAL SHUNT JamesH. Leonard, Philadelphia, Pa., assignor to I-T-E 'Circuit BreakerCompany, Philadelphia, Pa. Filed June 5, 1958, Ser. No. 740,041 3Claims. (Cl. 200'88) My invention relates to circuit breakers in generaland is more particularly directed to a novel shunting means forby-passing the bimetal time delay trip element of the circuit breakerupon the occurrence of a severe overload condition.

Molded case circuit breakers are provided with a time delay trip unitusually in the foirn of a bimetallic element and an instantaneous tripelement which is in the form of a yoke armature combination. On theoccurrence of an overcurrent, the deflection of the bimetal will beeffective to delatch the cradle mechanism and on the occurrence of afault current the magnetic yoke will be sufiiciently energized toattract its armature thereby resulting in delatching of the cradlemechanism to effect contact disengagement.

-It has been found that the bimetal will be permanently deformed if itis subjected to excessive currents. Some circuit breakers of the priorart have included circuits which shunt current so as to by-pass thebimetal upon the actuation of the instantaneous trip unit. In this waythe bimetal is protected from excessive current from the movement thatthe armature is attracted by the yoke. However, the armature is of asubstantial mass so that its operating time is not instantaneous.

It has also been found that upon the occurrence of a short circuitcondition the bimetal shunt circuit is not actuated by the instantaneoustrip unit in a sufficiently short interval of time so as to preventburn-out or distortion due to excessive heating in the case of adirectly heated bimetal. The problem is particularly severe in circuitbreakers having a low continuous circuit rating, hence a high resistancebimetal.

The circuit breaker of the instant invention is provided with a shuntingcircuit which is actuated by the bimetal itself. That is, the free endof the bimetal carries a contact which upon suicient deection of thebimetal, engages a contact in a shunt circuit which is completed whenthe two contacts are in engagement. The shunt circuit is not completeduring normal heating of the bimetal but is closed when there isover-heating of the bimetal but is closed when there is over-heating ata time before burn-out or distortion set in. Thus the shunt does notcarry current for an extended period of time but merely for some timeless than it takes the circuit breaker to open after being hit by ashort circuit or severe lfault condition. The bimetal actuated shunt, inaddition to its superior electrical qualities over that of theinstantaneous trip operated shunt, offers the advantages of compactnessIand fewer number of parts.

The shunt comprises a member which is securely fastened at one end andextends parallel to the bimetal. A contact is secured to the shunt atits free end and is positioned to be engaged by a contact carried by thebimetal, at the free end thereof, when the deflection of the bimetalreaches a predetermined point.

In order to prevent a reverse deflection of the bimetal under extremelyhigh current conditions, the shunt is constructed of a yieldablematerial. However, the material is sufficiently resistant to deflectionto prevent contact rebound and maintain contact pressure sufficient toestablish a low resistance juncture.

Accordingly, a primary object of the instant invention is to provide -anovel shunting circuit for the thermal time delay tripping element of acircuit breaker.

ICC

Another object of this invention is to provide a directly heated thermaltime delay trip element and a shunt therefor which are both mechanicallyindependent of the instantaneous trip device although both act on thesame common tripper bar.

Still another object is to provide a bimetal actuated bimetal shunt forthe directly heated bimetallic element of an instantaneous trip unit ofa molded case circuit breaker.

These as Well as other objects of the instant invention shall becomereadily apparent after reading the following description of theVaccompanying drawings in which:

FIGURE l is a top view of a three pole circuit breaker, including mynovel bimetal actuated bimetal bypass, with the cover removed.

FIGURE 2 is a side sectional view of the circuit breaker taken alongline 2 2 of FIGURE l, and illustrates the operating mechanism after thecircuit breaker has been tripped due to an overcurrent.

FIGURE 3 is a perspective view illustrating the mechanical independenceof the time delay bimetal and its shunt from the instantaneous tripunit.

FIGURE 4 is an end view of the overcurrent device.

FIGURE 5 is a side view of the novel bimetal actuated bimetal shunt.

FIGURE 6 is a view taken in the direction of the arrows 6-6 of FIGURE 5.

FIGURE 7 illustrates a modification of this invention wherein a movingshunt is carried by the bimetallic element.

Referring first to FIGURES l and 2 showing a three pole embodiment of acircuit breaker in which my invention can be adapted, the housing 20 ofthe circuit breaker 10 is preferably made of a plastic substance and isprovided with appropriate openings 21 and 22 through which the circuitbreaker terminals 25-26, respectively, `are substantially brought out ofhousing 20 to be engaged by the line terminals of the line to beprotected. This circuit breaker may be of the type shown in U.S. Patent2,673,908 to I. C. Brumfield entitled Instantaneous Trip Circuit andassigned to the assignee of the instant application.

The housing 20 consists of two sections, a base 20a is a section of thehousing 20 on which the various components of the circuit breaker 10 aremounted as hereinafter described and a cover 20b which completely closesthe circuit breaker 10 by tightly engaging the base 20a.

In the three pole circuit breaker 10 which is being considered for thisexample, there will be three sets of circuit breaker terminals 25 and26. However, for the sake of clarity, only the center phase B of thethree pole circuit breaker 10 having phases A, B and C will bedescribed.

`Considering then this center phase B of the three pole circuit breaker10, the circuit breaker terminal 25B rests against an extending shoulder28B of molding 20a. Shoulder 28B is perforated to receive threadedinsert 29B which eventually receives a bolt (not shown) to secure 'theline terminal (not shown) to circuit breaker terminal 25B. As previouslymentioned, circuit breaker terminal 25B extends through opening 21B intobase 20a. Circuit breaker terminal 25B is shaped like -an angle, oneside 30B of the angle being used to receive a line terminal (not shown),while the other side 31B is soldered or in any other way connected to apigtail or conductor 35B.

Pigtail 35B is rigidly secured to cross member 300B mounted to bimetal38B at the calibration screw 43B. As best seen in FIGURES 3 through 6,the L-shaped thermal responsive means 38B has one leg thereof positionedon top of the substantially U-shaped magnetic yoke 200. A screw 201 ispassed through the leg of fixed shunt member 301B, through one leg ofthe bimetal 38B through magnet-ic yoke 200 into the molding 20a. Thus,the screw 201 secures both the bimetallic element 38B and the magneticyoke 200 to the base molding 20a and also serves to electrically connectthe terminal 48B to the bimetallic element 36B. Big-tail 52B is solderedor otherwise Vsecured to the diagonally extending tip 48B of shuntmember 301B. Thus, a com plete current path is -provided from thepigtail 52B to the terminal 48B and out the pigtail 35B to thereby forma single turn for the energization of the magnetic yoke 200.

A pivotally mounted shaft 203 mounted in bearings 204, 205 contains wirespring 206. A barrier plate 209 positioned Within appropriate recessesof the groove in base molding 20a for the overcurrent device serves as astop for one end of the wire spring 206.

The armature 211 is secured to the rotatably mounted shaft 203 at thearea which contains the wire spring 206 land serves as a stop for theopposite end of this Wire spring. It will be noted that the wire spring206 may be mounted on either side of lthe armature 211 rather than beingmounted in the center as shown in FIGURE 3. With only one end of thespring 206 engaging the armature 211, it will not be necessary to reducethe crosssectional `area of the shaft 203 to mount the spring. Thus, asbest seen in FIGURE 5, the armature 21.1 is biased in a counterclockwisedirection around the shaft 203 due to the wire spring 206. The bottomledge of the barrier 209 serves as ya stop to limit the counterclockwiserotation of the armature 211.

The enlarged magnetic section 213 of the armature 211 is positionedabovethe pole faces 214 and 215 of the magnetic yoke 200. On theoccurrence of a fault current, the single turn comprising the current owthrough the bimetal 38B will sufficiently energize the magnetic yoke 200so that the portion 213 of the armature 211 will be attracted toward thepole faces 214 and 215. That is, the armature 211 will be rotated in aclockwise direction against `the bias of the wire spring 206, Theprotruding portion 21B of the armature 211 will then be against theprotrusion 60B of the common tripper bar 65.

As will be apparent, the counterclockwise rotation of the common tripper4bar 65 will effect disengagement of the latch 147B--152B to therebyeffect disengagement of the cooperating contacts 77-85.

It will be noted that the movement of the Aarmature 211 when attractedby the magnetic pole 200 is completely independent of the movement ofthe bimetal 38B and hence, clockwise rotation thereof will result in lahammer blow on the protrusion 60B of the common tripper bar 65 to effectcontact disengagement. The portion 66B of `the common tripper bar 65 ispositioned in alignment with the adjustment screw 43B of the thermalelement 38B. Thus, on the occurrence of an overcurrent, the bimetal 38Bwill deflect to the right in the conventional manner as seen in FIGURE2, to thereby engage the portion 66B and cause counterclockwise rotationof the common tripper bar 65. It will be noted that when the circuitbreaker is tripped due to the occurrence of an overeurrent condition,the bimetallic element 38B will deflect to the right `and its 4movementwill be independent and unaffected by the instantaneous magnetic tripmeans 2011-211.

The common tripper bar 65 provided Aat phase B as above noted has anextending member having portions 60B and 66B which are respectivelyengaged by the portion 216 of the armature 211 `and the adjustment screw43B of the bimetal 38B.

The pigtail 52B to the fault current responsive means 38B and 211 iselectrically connected to the arm 71B at the end 70B thereof. Movablecontact `arm 71B is pivoted by means of the pivot pin 72B engaging`aligned openings 73B of the metallic `frame or support 75B. Contact arm71B is provided at its other end with a substantially rectangular shapedcontact slab 77B. Contact slab 77B made of good conducting material isrigidly secured to cont-act arm 71B by means of a rivet 78B or in anyother suitable way.

Stationary contact 80B consists of a rectangular section metallic member81B having at the end nearer to contact arm 71B a stationary contactslab JSSB'rigidly secured to member 80B. Member 81B is secured tohousing 20a of the circuit breaker through a screw 86B and 1a washer87B. Stationary contact V'80B is lalso provided with `a terminalextension 26, yan integral part of metallic member 81B, which extendsyfor 4a portion 90B out of housing 20a to permit by means of screw means(not shown) the connection of a line terminal .to circuit breakerterminal 26. Stationary contact 80B is further provided with an yarcextinguishing chamber B or `arc chute having a number of arcextinguishing plates 96B so that at ,the opening portion of the circuitbreaker the arc existing between contact slab 77B and contact slab 85Bis extingiished before producing damage to the contact slabs 77B and85B.

The operating mechanism of the circuit breaker, which forms no part ofmy present invention, is described in the aforementioned U.S. Patent2,673,908.

T-member `B is provided at its upper portion 122B with a substantiallyrectangular extension 131B. Upper portion 122B of T-member 120B isslotted in its mid portion and provided with raised member 132B cutoutfrom the upper portion 122B of T-member 120B which serves to be engagedby a plastic operating handle 135B tor manually opening and closing thecircuit breaker, as hereinafter described. One leg 155B of the V-shapedcradle B is shaped as shown in FIGURE 2 to engage a latch 147B. Latch147B is provided with a slot 148B engaged by pin 150B around which latch147B can rotate and can also have translational motion. Latch 147B isprovided with a pointed end 151B latched under norm-al conditions by alatch surface 152B on the tripper bar 65.

Latch surface 152B is composed of a thin strip of material on tripperbar 65 supporting the latch 147B. The leg 157B of Vshaped member 145B isprovided with a cylindrical hole engaged by a pivot pin l106B secured tothe raised portion B of frame 75B. Leg 157B 0f V-shaped member 145B isprovided at the bottom of the V with a shoulder extension 166B. Raisedportion 165B of frame 75B is provided with an opening through whichpasses contact slab 77B of movable contact arm 71B and provides a stop`for V-shaped cradle 145B.

Near the end 70B of movable contact arm 71B at which pigtail 52B isconnected, `an essentially rectangular section bar is rigidly secured tomovable contact arm 71B in any suitable way. Shaft or tie bar 1180 iscommon to all three phases A, B and C of the three-pole circuit breaker,being rigidly secured to the ends 70 of the movable contact arm 71 ofevery phase so that if one mov-able contact, for example, 71B, is movedwhether opened or closed, the other two movable contact arms 71A and 71Cwill simultaneously perform the same movements. The circuit breaker 10is also provided, in the vicinity of are chute 95B, with an insulation185B for completely insulating arc chute 95B.

Thus, it will be seen that when either the time delay or instantaneousovercurrent means rotates the common tripper bar 65, in a clockwisedirection, both the latch Y147B and 187B will be released and hence,spring 118 will drive the contacts '77 to 4disengaged' position.

As heretofore noted this trip of the circuit'breaker to the positionindicated in FIGURE Zby the releaseof the 'two latches can .be achievedby either an overcurrent which will cause delico-tion .of the bimetal38B to the right and result in engagement of the adjustment ,screw 43Bwith the protmsion 66B to cause counterclockwise rotation of the tripperbar 65 or due to a fault current condition wherein the single turn ofthe bimetal y38B will sutciently energize the magnetic pole 200 tothereby rotate the armature 211 in a clockwise direction yagainst: itsbias aosaeo 206 thereby bringing its extension 216 into engagement withthe protruding portion 60B to rotate the tripper bar in acounterclockwise direction.

Thus, it will be seen that with the novel overcurrent device of myinvention, the instantaneous trip means comprising the armature 213 andthe m-agnetic yoke 200 are mechanically independent of the time delaythermal means 38B and hence, the occurrence of a fault current or anovercurrent will result in a blow or force in one direction on thetripper bar 65 to result in the tripping of the circuit breaker.

Fixed shunt member 310B is generally L-shaped with the upwardlyextending arm thereof being positioned generally parallel to theupwardly extended leg of bimetal 38B when it is not deflected. A fixedshunt contact 302B issecured to the upper end of shunt member 301B andis positioned for engagement by movable contact 303B carried by thebimetal cross-member 300B.

When shunt contacts 302B and 303B are engaged a complete current pathbetween pigtails 43B and 52B which by-passes bimetal 38B is formed. Thiscurrent path ex* tends from pigtail 35B, through cross-member 300B,through shunt contacts 302B and 303B, through llow resistance fixedshunt 301B to pigtail 52B. Current flow is shunted through this pathsince fixed shunt 301B is of a much lower electrical resistance thanbimetal 38B.

Upon the occurrence of a mere overload condition the upper end ofbimetal 38B will slowly deflect to the right until adjusting screw 43Bengages portion 66B of tripper bar 65 and the cooperating contacts 77B,85B will be parted before shunting contacts 302B, 303B become engaged.

Upon the occurrence of a short circuit or other severe faultinstantaneous trip means 200-211 will act before screw 43B has engagedtripper bar 65. However, circuit interruption is not instantaneous sothat bimetal 38B is deflected beyond the point where screw 43B engagestripper bar 65 under mere overcurrent conditions. Bimetal 38B willcontinue to deflect until movable shunt contact 303B engages fixed shuntcontact 302B and the major portion of the circuit current now passesthrough shunt 301B rather than bimetal 38B. The spacing between shuntcontacts 302B and 303B is such that they will be engaged before burn-outor distortion of bimetal 38B can take place.

FIGURE 7 illustrates a variation of the bimetal shunting circuithereinbefore described. This latter circuit comprises a movable shuntingmember 400 secured at one end. 401 to the free end of bimetal 38B andcarrying movable shunt contact 402 at its other end. Movable shunt con.tact 402 as positioned to engage fixed shunt Contact 403 and when soengaged most of the phase current will bypass bimetal 38B by followingthrough stationary shunt 404 and movable shunt 400 now connected inseries.

Shunts 400 and 301B are both constructed of a low resistance materialwhich is sufliciently yieldable so as to prevent reverse deflection ofbimetal 38B when it is subjected to currents of high magnitude. Furtherthe material of shunts 400 and 301B is suiciently rigid so as to preventcontact rebound and maintain high contact pressure to provide a lowresistance joint.

In the foregoing, I have described my invention only in connection withpreferred embodiments thereof. Many variations and modifications of theprinciples of my invention within the scope of the description hereinare obvious. Accordingly, I prefer to be bound not by the specificdisclosure herein but only by the appending claims` I claim:

l. A circuit breaker having a pair of cooperable contacts; one of saidcontacts being biased to open position; a thermally responsive elementcomprising a bimetal; one end of said bimetal being rigidly supportedand the other end flexing when heated; said thermally responsive elementbeing connectible into an electric circuit to be protected by saidcircuit breaker; an electromagnet connected in electrical series withsaid thonmally responsive element; a trip latch engaging said biasedcontact to maintain said contact -in its contact engagement with theother of said cooperable contacts; the flexible portion of said bimetalwhen operated to a first predetermined position operating said triplatch to release said contact for operation by its bias; an amatureoperated by said electromagnet when fault current flows through saidelectric circuit and energizes said electromagnet; said armature whenoper-ated operating said trip latch; said circuit comprising a fixedshunt contact and a movable shunt contact; said movable shunt contactbeing carried by said bimetal and being operatively positioned to engagesaid fixed shunt contact when said bimetal is operated to said secondposition; a shunt circuit also including an L-shaped shunt member; oneleg of said shunt member being rigidly supported; said fixed shuntcontact being mounted near the free end of the other leg of said shuntmember; said member being comprised of a material having sufficientrigidity to prevent rebound of said shunt contacts and to maintain con*tact pressure between said shunt contacts; said member beingsufliciently yieldable to prevent a reverse deflection of said bimetal;said circuit breaker having the elements thereof operatively arranged sothat the free end of the other leg of said shunt member is free to bedeflected a substantial distance.

2. A circuit breaker having a pair of cooperable contacts; one of saidcontacts being biased to open position; a thermally responsive elementcomprising a bimetal; one end of said bimetal being rigidly supportedand the other end flexing when heated; said thermally responsive elementbeing connectible into an electric circuit to be protected by saidcircuit breaker; an electromagnet connected in electrical series withsaid thermally responsive element; a trip latch engaging said biasedcontact to maintain said contact in its contact engagement with theother of said cooperable contacts; the flexible portion of said bimetalwhen operated to a first predetermined position operating said triplatch to release said contact for operation by its bias; an armatureoperated by said electromagnet when fault current flows through saidelectric circuit and energizes said electromagnet; said armature whenoperated operating said trip latch; said circuit comprising a fixedshunt contact and a movable shunt contact; said movable shunt contactbeing carried by said bimetal and being operatively positioned to engagesaid fixed shunt contact when said bimetal is operated to said secondposition; a shunt circuit also including an L-shaped shunt member; oneleg of said shunt member being rigidly supported; said fixed shuntcontact being mounted near the free end of the other leg of said shuntmember; a first member mounted to the other leg of said bimetal near thefree end thereof and extending transverse to the plane of movement ofsaid bimetal; said movable shunt contact being mounted to said firstmember; said member being comprised of a material having suflicientrigidity to prevent rebound of said shunt contacts and to maintaincontact pressure between said shunt contacts; said member beingsufficiently yieldable to prevent a reverse deflection of said bimetal;said circuit breaker having the elements thereof operatively arranged sothat the free end of the other leg of said shunt member is free to bedeflected a substantial distance.

3. A circuit breaker having a pair of cooperable contacts; one of saidcont-acts being biased to open position; a thermally responsive elementcomprising a bimetal; one end of said bimetal being rigidly supportedand the other end flexing when heated; said thermally responsive elernent being connectible into an electric circuit to be protected by saidcircuit breaker; an electromagnet connected in electrical series withsaid thermally responsive element; a trip latch engaging said biasedcontact to maintain said contact in its contact eng-agement with theother of said cooperable contacts; the flexible portion of said bimetalwhen operated to a first predetermined position operating said triplatch to release said contact for operation by its bias; an armatureoperated `by said electromagnet when fault current flows through saidelectric circuit and energizes said electromagnet; said armature whenoperated operating said trip latch; a circuit comprising a fixed shuntcontact and a movable shunt contact; said movable shunt contact beingycarried by said bimetal and being operatively positioned to engage saidXed shunt contact when said bimetal is operated to said second position;said shunt circuit also including .a shunt member secured at one endthereof `to said other end of said bimetal and extending toward said oneend of said bimetal; said movable shunt contact being secured .to asecond end of said shunt member; said member being comprised of amaterial having suciently rigidity to prevent rebound of said shuntcontacts and to maintain contact pressure between said shunt Acont-acts;said member being sufciently yieldable `to prevent a reverse deflec- 8tion of said bimetal; said shunt member being connected into saidelectric circuit only when said shunt contacts are in engagement; saidcircuit breaker having the elements thereof operatively arranged so thatthe free end of 4the other leg of said shunt member is free to bedeflected -a substantial distance.

References Cited in the tile of this patent UNITED STATES PATENTS1,966,444 Guett July 17, 1939 2,328,458 Jackson Aug. 31, 1943 2,357,151Von Hoor-n Aug. 29, 1944 2,362,855 Stimson Nov. 14, 1944 2,491,959 DyerDec. 20, 1949 2,754,392 Bendik July Al0, 1956 2,764,650 Hodson Sept. 25,11956 2,845,507 Brumfield July 29, 1958

